The Americans With Disabilities Act of 1990 ("ADA") requires many public places to provide assistive listening systems for use by hearing impaired individuals. Assistive listening systems transmit audio through an alternative medium to individuals equipped with appropriate receivers so as to permit those individuals to hear the audio at a sufficient volume to compensate for some heating disability. According to figures from the National Technical Institute for the Deaf in Rochester, N.Y., of the 25 million hearing impaired persons in the United States, only two million are profoundly deaf. Many of the remaining 23 million could benefit from the use of assistive listening devices.
The use of infrared light to transmit a frequency modulated pulse wave has become a popular method for transmitting audio from assistive listening systems. Although experiments in data communication using light radiation can be traced back to Alexander Graham Bell in 1880, infrared communication did not become commercially possible until the development of infrared light emitting diodes ("LEDs") in 1963. Since then, infrared technology has proven to be an efficient and economical method of audio transmission and, unlike radio-based technologies, offers security from unwanted eavesdropping and permits multiple systems within the same building to operate on a single standard frequency.
All infrared assistive listening systems operate on the same general principle. Audio is taken from its source, converted to a frequency-modulated pulse wave, transmitted as light radiation by infrared LED emitters, and is ultimately received by a headset receiver that converts the light radiation back to audio to be delivered to the listener's ear.
Infrared assistive listening systems for home use or for commercial theatrical use have been available on the market for some time, but systems compatible for medium-sized locations, such as courtrooms, classrooms, conference rooms and the like, have been largely non-existent. It is precisely these locations, however, that must be equipped with assistive listening systems to secure compliance with the ADA.
Theatrical systems are not appropriate for most medium-sized locations. Theatrical systems tend to be bulky, non-portable, and expensive. In addition, they are usually configured to service audience seating, and perform poorly in locations structured "in the round", such as conference rooms.
At the other extreme, small systems for home use are also incapable of satisfactorily servicing medium-sized locations. These systems are normally designed to serve as wireless headphones for television or home stereo listening. They usually do not have a microphone capability and, more importantly, only provide coverage within about a fifteen by eight foot range, the typical area of a living room.
A few manufacturers have, however, introduced infrared assistive listening systems targeted for installation in medium-sized locations. These systems unfortunately suffer from several serious deficiencies. For example, these systems only provide suitable audio coverage within twenty-five feet or less, a range too limited for most classrooms or courtrooms.
In addition, these current systems do not address the special needs for uses intended for medium-sized locations. Unlike, home or theater applications, where the audio is usually from a fixed source, infrared assistive listening systems for use in medium-sized locations must be able to accommodate the dynamic interplay of a variety of speakers situated in many different parts of the room. Current medium-sized systems, however, do not adequately pick up distant speakers over competing noise sources, such as air conditioners or traffic rumble. Nor do they adequately compensate for the wide range in volume levels present in the conference or classroom setting.
Also, the continuous transmission aspect of current medium-sized systems is problematic. Situations often arise, for example, in conferences or trials, where a subset of speakers wish to speak privately. To accommodate such situations, today's medium-sized systems require a full power shutdown.